White Paper, Rev. 0 Determination of External Dose from Thorium Metal Machining - A TBD-6000 Approach April 2014 

Determination of External Dose 

from Thorium Metal Machining - A TBD-6000 Approach 

NIOSH White Paper, Rev. 0 

April 17, 2014 

Sam Glover and Dave Allen, DCAS 

Page 1 of 4 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions with the 

ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their 

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White Paper, Rev. 0 Determination of External Dose from Thorium Metal Machining - A TBD-6000 Approach April 2014 

Introduction 

The basic methods used for the determination of external dose from handling and machining operations involving 

uranium metal developed in TBD-6000 were utilized to determine the external dose from thorium metal 

operations. The thorium metal was assumed to be in 100% equilibrium with its progeny at the time of handling. 

MCNP6 was used to determine the average dose per photon emission from the decay of 232Th and its progeny; the 

average dose per electron emission from the decay of 232Th and its progeny; and finally the bremsstrahlung dose 

per electron emission from the decay of 232Th and its progeny. These values were scaled in accordance with data 

obtained from the Joslyn facility with regards to rod sizes that were handled. Dose rates were determined for the 

same periods as used in TBD-6000 and are to be scaled according to the specific operational details for a facility.

 Files 

 thor_rod_gamma_2014.i (MCNP6 input file for photon dose) 

 thor_rod_gamma_2014.io (MCNP6 output file for photon dose) 

 thor_rod_beta_2014.i (MCNP6 input for file for beta dose) 

 thor_rod_beta_2014.io (MCNP6 output file for beta dose) 

 thor_rod_brem_2014.i (MCNP6 input file for bremsstrahlung dose) 

 thor_rod_brem_2014.i o (MCNP6 output file for bremsstrahlung dose) 

 electron spectra 4-8-2014 for thorium chain.xls (summary of electron emissions spectra from 232Th in 

equilibrium with all progeny) 

 thorium dose summary .xls (summary of the dose from all sources and the beta and gamma emission 

lines used) 

MCNP 6 Modeling 

A thorium rod 50 in. long, with a radius of 1 7/8 in., a density of 11.7 g/cm3

 was modeled using data included in 

the references files for 232Th in equilibrium with its progeny. As described above, these were the dimensions of 

rods actually handled at Joslyn. Using the decay information from Thorium and the data provided in the files, it 

was determined that there are 4 betas and 3.465 photons per 232Th decay (including from progeny). The 26.469 

Kg of 232Th was determined to have a decay rate of 1.08x108

 Bq (based solely on the 232Th) using the dose 

determined from the MCNP 6 runs, which converted the photon and beta spectra into units of dose per photon, 

and electron using the ICRP 74 Tables A.43 (for pGy/electron) and ICRP A.17 (for photons to pSv/photon). See 

worksheet Summary from file Thorium Dose Summary.XLS for complete calculation details that are included in 

part in Tables 1 and 2. Table 1 provides a summary of the individual dose components from beta dose and 

gamma dose from the Bremsstrahlung and photon emissions of thorium and its progeny. Table 2 summarizes the 

TBD-6000 equivalent doses from these emissions whole body photon dose, whole body beta dose, and beta dose 

to the hands and forearms. 

Page 2 of 4 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions with the 

ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their 

technical support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken on technical 

issues prepared by NIOSH or its contractor. NOTICE: This information is protected by the Privacy Act 5 USC §552a; disclosure to any third party 

without the written consent of the individual(s) to whom the information pertains is strictly prohibited 
 

 

       

                 

     

                 

     

     

       

        

       

       

         

White Paper, Rev. 0 Determination of External Dose from Thorium Metal Machining - A TBD-6000 Approach April 2014 

Table 1: Summary of Dose rates from thorium metal rod 

Doses from MCNP 6 Runs

Beta Dose Bremsstrahlung Photon

(thor_rod_beta_2014.io) (thor_rod_brem_2014.io) (thor_rod_gamma_2014.io)

1 cm 1 cm 1 cm

6.45E‐05 pGy/electron 2.65E‐06 pSv/electron 4.03E‐04 pSv/photon

4.31E+08 electrons/sec 4.31E+08 electrons/sec 3.74E+08 photons/sec

2.78E+04 pGy/s 1.14E+03 pSv/s 1.51E+05 pSv/s

1.00E+01 mrad/hr beta 4.12E‐01 mrem/hr 5.42E+01 mrem/hr

1 ft 1 ft 1 ft

8.80E‐06 pGy/electron 2.16E‐07 pSv/electron 3.20E‐05 pSv/photon

4.31E+08 electrons/sec 4.31E+08 electrons/sec 3.74E+08 photons/sec

3.80E+03 pGy/s 9.30E+01 pSv/s 1.20E+04 pSv/s

1.37E+00 mrad/hr beta 3.35E‐02 mrem/hr 4.30E+00 mrem/hr

1 m 1 m 1 m

1.10E‐06 pGy/electron 4.06E‐08 pSv/electron 5.85E‐06 pSv/photon

4.31E+08 electrons/sec 4.31E+08 electrons/sec 3.74E+08 photons/sec

4.74E+02 pGy/s 1.75E+01 pSv/s 2.19E+03 pSv/s

1.71E‐01 mrad/hr beta 6.31E‐03 mrem/hr 7.87E‐01 mrem/hr

These data were converted to units of dose to machining operations in an identical fashion as used for TBD-6000 including the categories of workers and 

assumptions (see worksheet Summary from file Thorium Dose Summary.XLS) for complete calculation details. 

Table 2: Summary of doses using a TBD-6000 methodology for thorium metal handling 

Summary of dose rates (per hour) for thorium metal handling

Distance 1 cm 1 ft 1 m

Photon dose 5.46E+01 4.34E+00 7.93E‐01 mrem/hr

Beta dose 1.00E+01 1.37E+00 1.71E‐01 mrad/hr

Thorium using TBD‐6000 Approach‐ full year‐based on 40 hour work week

operator gen lab super clerical

Photon whole body (mrem/yr) 4335.734 7.93E+02 396.5633 39.65633

beta whole body (mrad/yr) 1366.28 683.1399 68.31399 0

beta hands & forearms (mrad/yr) 10017.01 5008.507 500.8507 0

Thorium using same technique ‐ 24 hr dose rates

operator gen lab super clerical

Photon whole body (mrem/24 hrs) 52.03 9.52 4.76 0.48

beta whole body (mrad/24 hours) 16.40 8.20 0.82 0.00

beta hands & foreams (mrad/24 hours) 120.20 60.10 6.01 0.00

Page 3 of 4 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions with the 

ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their 

technical support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken on technical 

issues prepared by NIOSH or its contractor. NOTICE: This information is protected by the Privacy Act 5 USC §552a; disclosure to any third party 

without the written consent of the individual(s) to whom the information pertains is strictly prohibited 
 

 

       

       

         

        

White Paper, Rev. 0 Determination of External Dose from Thorium Metal Machining - A TBD-6000 Approach April 2014 

Application for Dose at Joslyn 

In accordance with records from Joslyn, thorium rods were handled on two occasions, all in very limited 

quantities. These included the following: 

Operations in May 1946 included the Medart straightening and centerless grinding of 6 thorium rods (srdb 80029, 

pages 2 and 3 and 80171, page 3). In early 1947, Joslyn centerless ground and Medart straightened (three times 

each) 5 thorium rods (SRDB 81068, page 2). Because of the very limited amounts of thorium used in the 

experiments, a conservative estimate of 2.5 work days each for 1946 and 1947 operations has been assumed. 

As described in the (thorium dose summary.xls) file, the thorium rod size was estimated as being 50 in. in length 

with a diameter of 1 7/8 in., a density of 11.7 g/cm3

 for an estimated 26.469 Kg of thorium metal per rod. 

Two and one-half work days during this time period corresponds to 24 hours of work (2400 hrs/250 work 

days*2.5 work days). Therefore the dose from thorium for both 1946 and 1947 at Joslyn was determined to be 

shown in Table 3. 

Table 3: External dose per year for 1946 and 1947 at Joslyn from handling thorium metal 

Thorium using same technique ‐ 24 hr dose rates

operator

Photon whole body (mrem/24 hrs) 52.03

beta whole body (mrad/24 hours) 16.40

beta hands & foreams (mrad/24 hours) 120.20

Page 4 of 4 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions with the 

ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their 

technical support and review contractors) positions unless specifically marked as such. This document represents preliminary positions taken on technical 

issues prepared by NIOSH or its contractor. NOTICE: This information is protected by the Privacy Act 5 USC §552a; disclosure to any third party 

without the written consent of the individual(s) to whom the information pertains is strictly prohibited